add nullable type

src/Php/TypeAnalyzer.php

@@ -2,10 +2,17 @@
 
 namespace Rector\Php;
 
+use Nette\Utils\Strings;
+
 final class TypeAnalyzer
 {
     public function isPhpReservedType(string $type): bool
     {
         return in_array($type, ['string', 'bool', 'mixed', 'object', 'iterable', 'array'], true);
     }
+
+    public function isNullableType(string $type): bool
+    {
+        return Strings::startsWith($type, '?');
+    }
 }

src/Rector/Dynamic/ReturnTypehintRector.php

@@ -5,6 +5,7 @@ namespace Rector\Rector\Dynamic;
 use PhpParser\Node;
 use PhpParser\Node\Identifier;
 use PhpParser\Node\Name\FullyQualified;
+use PhpParser\Node\NullableType;
 use PhpParser\Node\Param;
 use PhpParser\Node\Stmt\Class_;
 use PhpParser\Node\Stmt\ClassLike;
@@ -150,8 +151,11 @@ CODE_SAMPLE
             return $classMethodNode;
         }
 
+        // @todo possibly decouple to smth like IdentifierRenamer?
         if ($this->typeAnalyzer->isPhpReservedType($newTypehint)) {
             $classMethodNode->returnType = new Identifier($newTypehint);
+        } elseif ($this->typeAnalyzer->isNullableType($newTypehint)) {
+            $classMethodNode->returnType = new NullableType('\\' . ltrim($newTypehint, '?'));
         } else {
             $classMethodNode->returnType = new FullyQualified($newTypehint);
         }

tests/Rector/Dynamic/ReturnTypehintRector/Correct/correct3.php.inc

@@ -0,0 +1,10 @@
+<?php declare(strict_types=1);
+
+namespace SomeNamespace;
+
+class SomeClass
+{
+    public function nullable() : ?\SomeType
+    {
+    }
+}

tests/Rector/Dynamic/ReturnTypehintRector/ReturnTypehintRectorTest.php

@@ -22,6 +22,7 @@ final class ReturnTypehintRectorTest extends AbstractRectorTestCase
     {
         yield [__DIR__ . '/Wrong/wrong.php.inc', __DIR__ . '/Correct/correct.php.inc'];
         yield [__DIR__ . '/Wrong/wrong2.php.inc', __DIR__ . '/Correct/correct2.php.inc'];
+        yield [__DIR__ . '/Wrong/wrong3.php.inc', __DIR__ . '/Correct/correct3.php.inc'];
     }
 
     protected function provideConfig(): string

tests/Rector/Dynamic/ReturnTypehintRector/Wrong/wrong3.php.inc

@@ -0,0 +1,10 @@
+<?php declare(strict_types=1);
+
+namespace SomeNamespace;
+
+class SomeClass
+{
+    public function nullable()
+    {
+    }
+}

tests/Rector/Dynamic/ReturnTypehintRector/config.yml

@@ -4,3 +4,4 @@ services:
             'SomeNamespace\SomeClass':
                 'parse': 'array'
                 'resolve': 'SomeType'
+                'nullable': '?SomeType'